Post-traumatic stress disorder (PTSD) is unique among the psychiatric disorders, in that it requires an environmental exposure (trauma) for diagnosis, and is thus ideal for investigating the gene-environment (G x E) predictors of pathology1. Despite the high national prevalence of trauma, studies such as the South African Stress & Health Study (SASH) found that only 2.3% of South Africans suffer from PTSD in their lifetimes (2,3). PTSD and depression have been found to be highly co-morbid4,5 and there is evidence to suggest significant gender-related variation in these disorders2,6-9. Overall, females have been found to be at higher risk than males, which may be compounded by the high prevalence of intimate partner violence (IPV) perpetrated again women10-12. Pregnant women, in particular, have been shown to be particularly vulnerable to IPV and its adverse mental and physical health outcomes (10-12). While a number of studies have been conducted in the developed, high-income world to investigate the etiology of these disorders (13-21), there is a paucity of data in developing, low- to middle-income (LMIC) countries. Nonetheless, there is evidence to suggest an element of heritability in individuals with PTSD and co-morbid depression (4,6,22-29), which may be due to genetic predisposition or to environmental conditioning such as learned behaviour. In this study, we shall examine the hypothesis that vulnerability to PTSD and co-morbid depression results from interactions between specific candidate genetic polymorphisms and environmental/psychological risk factors, which combine to enhance the risk for PTSD and co-morbid depression following trauma. Pregnant female South Africans, aged 18-65, will be recruited from specified community health centres. Those who wish to participate will complete a battery of self-report measures, including the Modified PTSD Symptom Scale (MPSS), Childhood Trauma Questionnaire (CTQ), Beck Depression Inventory (BDI-II), MINI (Mini International Neuropsychiatric Interview) Depression Scale, Intimate Partner Violence (IPV) Questionnaire and Clinician-Administered PTSD Scale (CAPS). Each participant will also be asked to provide a saliva sample for DNA extraction and genetic analysis. Despite the adversity faced by many Africans and South Africans, some cope and function remarkably well. Thus, identifying genetic or other factors that allow these individuals t cope may elucidate the underpinnings of resilience, which could inform the search for novel preventative and therapeutic interventions for these prevalent and debilitating disorders.